Effect of Temperature and Frequency on the Viscoelastic Behavior of Commercial 6082 (Al-Mg-Si) Alloy

The viscoelastic response of pure Al and commercial 6082 and 6082-T6 (Al-Mg-Si) alloys is measured with dynamic-mechanical analyzer as a function of temperature (ranging from 35 to 425 degrees C) and loading frequency (ranging from 0.01 to 100 Hz). The measured data (the storage modulus, loss modulus, and mechanical damping) are compared to available transmission electron microscopy and differential scanning calorimetry data, to ascertain whether unexplained variations of the viscoelastic behavior of the alloys can be correlated to phase transformations. The results suggest that some of these variations may be controlled by the formation and dissolution of metastable phases, such as Guinier-Preston (GP) zones and phases beta '', beta ', and B '. Indeed, GP zones and phase beta '' have been reported to control other mechanical properties. However, due to the high complexity of the aging path of Al-Mg-Si alloys, with formation and dissolution reactions of many precipitate types overlapping along wide temperature intervals, further research is necessary to establish unequivocally the contribution of each individual phase transformation to the overall viscoelastic behavior. Finally, an internal friction peak related to grain boundary sliding is significantly smaller in the alloys compared to pure Al, probably because the precipitates pin the grain boundaries.